package Year22_Month03.day13;

import java.util.Scanner;

public class Main2 {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int col = sc.nextInt();//行
        int row = sc.nextInt();//列
        int[][] arr = new int[col][row];
        int count = 0;
        for (int i = 0; i < col; i++) {
            for (int j = 0; j < row; j++) {
                if(arr[i][j] == 0){
                    //如果等于0，那么可以放蛋糕
                    count++;
                    //然后行和列进行限制
                    if(i + 2 < col && arr[i+2][j] == 0){
                        arr[i + 2][j] = 1;
                    }
                    if(j + 2 < row && arr[i][j + 2] == 0){
                        arr[i][j + 2] = 1;
                    }
                }
            }
        }
        System.out.println(count);
    }
}
